The invention relates generally to an ink jet printer, and, in particular, to the structure of a carriage having an ink jet printing head (hereinafter referred to simply as the "head") of the ink jet printer attached thereto. More specifically, the invention is directed to a new carriage structure for preventing play between the carriage and hence the head, and a guide shaft of the carriage; a new carriage structure which also allows for connecting the head to the carriage in a manner where it may be easily released and reattached to the carriage.
As is known in the prior art, and in particular, as is depicted in FIGS. 20 and 21, a conventional ink jet printer generally includes: a guide shaft 1101 extending in a direction orthogonal to a direction Y in which paper P is forwarded; a carriage 1102 mounted on guide shaft 1101 for reciprocal motion along guide shaft 1101 as indicated by arrow X1-X2 while guided by guide shaft 1101. An ink jet head 1103 is attached to carriage 1102 and prints ink drops on paper P by jetting ink. A number of nozzles n are formed on the surface 1103a of head 1103 facing paper P. Ink is selectively jetted out of nozzles n to make predetermined printed ink dots forming a printed image.
Carriage 1102 is slidable along guide shaft 1101. Therefore, a slight clearance is generally provided between guide shaft 1101 and the bearing portion of carriage 1102. As a result, unless made to a precise measurement, carriage 1102 may, in some cases, rotate (play) about an axis orthogonal to the plane of paper P, or in other words, with respect to guide shaft 1101, in the direction indicated by arrows T1 and T2. For example, carriage 1102 may, in some cases, slightly rotate in the direction of arrow T1 when moving in the direction of arrow X1 and slightly rotate in the direction of arrow T2 when moving in the direction of arrow X2.
When carriage 1102 rotates (plays) when moving in both directions this way, head 1103 also rotates, and the position of nozzles n are thus, also slightly displaced from a position parallel with guide shaft 1101. As a result, an inherent problem with this system is that the printing quality diminishes due to this misalignment. As shown in FIG. 20 in particular, in the case where head 1103 has a plurality (three in FIG. 22) of nozzle arrays N1, N2, N3 arranged side by side in the direction parallel with guide shaft 1101, also known as the carriage moving direction, the diminishment of printing quality may be aggravated. That is, when head 1103 is rotated in the direction of either arrows T1 or T2, the amount of displacement of nozzles n in the direction Y is larger in nozzle arrays N1 and N3 because they are offset further from the axis of rotation than nozzle array N2 in the middle and closest to the axis of rotation.
An additional problem which may arise if carriage 1102 plays in the direction of either of arrows T1 or T2 when moving in the directions of arrows X1-X2, respectively, is that the printing noise may be increased by such play. To overcome these problems, play between carriage 1102 and guide shaft 1101 should be reduced or eliminated.
As shown in FIGS. 23-27, a printer known from Examined Japanese Patent Publication No. Sho. 62-52717 includes a structure in which a carriage 1108 is supported by a guide shaft 1104 so that play between carriage 1108 and guide shaft 1104 is reduced. Carriage 1108 is mounted to ball bearings 1105a, 1105b and 1105c. Ball bearings 1105a, 1105b, 1105c come in contact with guide shaft 1104 at a lower surface and obliquely at upper surfaces. A slide bearing 1107 comes in contact with a flat portion 1104a of guide shaft 1104 while biased onto guide shaft 1104 by a flat spring 1106.
Further, as shown in FIG. 26, it is known from Unexamined Japanese Patent Publication No. Hei. 2-188283 to mount a carriage 1109 about a guide shaft 1110. In this case, a magnet 1111 is mounted on carriage 1109. Play of carriage 109 with respect to guide shaft 1110 is reduced or eliminated by utilizing the magnetic attracting force (biasing force) obtained by arranging magnet 1111 at a portion of carriage 1109 confronting guide shaft 1110.
On the other hand, another conventional ink jet printer well known in the prior art has the head attached to the carriage in a manner so as to be releasable and reattachable with respect to the carriage. If such a design is adopted for a printer, wiring for driving the nozzles on the head must be devised since the carriage and the head cannot be directly connected by means of solder or the like if it is to be removable.
Thus, as shown in FIG. 27, it is known from Unexamined Japanese Patent Publication No. Hei. 3-104643 to mount a carriage 1112 on a guide shaft 1110. An end 1113 of an FPC (Flexible Printed Cable) is attached to a carriage 1112 and a board 1115 is attached to a head 1114. Board 1115 is connected to end 1113 of the FPC so as to be in pressure contact therewith. Head 1114 is releasably attached to carriage 1112. It may be noted that the other end of the FPC is typically connected to a control board of a printer main body.
In such a structure, end 1113 of the FPC must be reliably brought into pressure contact with board 1115. In the structure disclosed in the aforementioned patent publication, a hook member 1116 for fixing head 1114 to carriage 1112 is biased in a direction to cause hook member 1116 to grasp head 1114 by a spring 1117, whereby board 1115 is brought into pressure contact with end 1113 of the FPC in a reliable manner.
The prior art devices have been satisfactory, however when one attempts to achieve the object of eliminating play between the carriage and the guide shaft as well as the object of releasably attaching the head to the carriage at the same time, the biasing member for eliminating the play between the carriage and the guide shaft (i.e., flat spring 1106 or magnet 1111 in the prior art, FIGS. 23 through 25 and 26, respectively) and the biasing member for bringing the board of the head into pressure contact with the FPC (i.e., spring 1117 of the prior art, FIG. 27) must be formed as separate components. In the conventional examples, the number of parts and the complexity would be increased, which in turn increases the cost and size of the carriage and hence the printer. This is yet another problem to be overcome.
Accordingly, a printer that overcomes the aforementioned disadvantages and limitations, which readily minimizes carriage play against the guide shaft and allows for easy removal and reattachment is desired.